The story might revolve around a situation where Natsu Dragneel is in love with someone and has to prove himself worthy of being chosen. He could use his fire - based magic skills to protect the person he loves and win her heart through his heroic deeds.
Perhaps it's a story set in a world full of magic and danger. Natsu Dragneel, being a powerful wizard, catches the eye of a girl. However, there are many obstacles in their way, like dark magic forces trying to keep them apart. And the whole 'choosing you' part could be about the girl finally choosing to stand by Natsu despite all the difficulties.
Well, it could be about a girl who has to choose between Natsu Dragneel and someone else. Maybe she meets Natsu in a magical adventure and gradually falls in love with his brave and warm - hearted nature.
It could be another male character who is also interested in the same person as Natsu. This would create a love triangle. He might be from a different guild or have a different type of magic, and the competition between him and Natsu for the girl's love would be a major part of the story.
It could be a really interesting crossover. Natsu is from 'Fairy Tail' with his powerful fire magic and hot - tempered nature. Sakura from 'Naruto' is a strong - willed kunoichi. Maybe in the fanfic, they meet in a strange new world created by some magical or ninja - related event. They could start off as rivals, not understanding each other's powers at first. But as the story progresses, they learn from each other and combine their skills to face a common enemy.
One idea could be Natsu from Fairy Tail finding himself in a parallel universe where he is an Etherious. He has to deal with the new powers and the darker side of himself while still trying to find his way back home. Another could be an Etherious teaming up with Natsu to fight a common enemy that threatens both their worlds. Maybe a powerful dark mage who wants to use the power of the Etherious and also destroy Fairy Tail.
A common plotline is the rescue mission. His friends from Fairy Tail band together to find and save him. Another is Natsu trying to break free on his own. He might use his fire magic in creative ways to escape his bonds.
Perhaps in the fanfiction, a cold - personality Natsu has lost his memories of his former self. He becomes a loner who is feared by many because of his icy demeanor. The story could then revolve around a character trying to help him regain his memories and bring back his old self. For example, Lucy could find an ancient spell that might restore his memories but has to go through many trials to use it.
A theme that is quite prevalent is the idea of sacrifice. In many fanfictions, either Natsu or Lucy is put in a position where they have to sacrifice something for the other. It could be their own safety, their magic, or their dreams. Also, the theme of growth is common. They both grow as characters, learning more about themselves and each other as the story progresses. This growth can be in terms of their magical abilities, but also in their emotional maturity.
Well, a common theme might be the idea of the underdog. Harry was an underdog in the wizarding world at first, and Natsu is also someone who has to fight hard against strong opponents. In these fanfictions, this theme could be explored more deeply. Also, the concept of family could be a theme. Natsu has his own idea of family within Fairy Tail, and Harry has his friends as a sort of surrogate family. The fanfiction could blend these two ideas together.
One plot idea could be that Natsu's little sister discovers a new and powerful form of magic that no one has ever seen before. She then has to learn to control it while also facing off against an evil wizard who wants to steal her power for himself. Another idea is that she goes on a journey to find out more about their family's past, which leads her to uncover long - lost secrets and reunite with long - lost relatives.
Well, I'm not sure how widespread it is, but it's possible to find such fanfiction. Writers often like to mash - up different universes to create something new. In a 'Harry Potter is Natsu Dragneel' fanfic, you might expect to see Harry with Natsu's determination and love for his friends translated into the context of the wizarding world. Maybe he'd be more brash and use his 'fire - like' magic in a more aggressive way like Natsu does.
One interesting crossover could be a battle scenario where Natsu's fire - based powers from Fairy Tail are pitted against the devils in Highschool DxD. His dragon slayer magic might give him an edge against some of the lower - level devils.